A new study from the US showed that two popular weight loss methods, one using the obesity treatment weight-loss pill orlistat plus a low-fat diet and another just based on a low carb diet were equally effective at helping people lose significant amounts of weight, but in a surprising twist found that that the low carb diet was much better at helping them lower blood pressure.

Researchers from the Veterans Affairs (VA) Medical Center and Duke University Medical Center, both in Durham, North Carolina, reported their findings in a study published online on 25 January in the Archives of Internal Medicine. The Department of Veteran Affairs paid for the research.

Lead author Dr. William S. Yancy Jr, an associate professor of medicine at Duke, said their findings send an important message to people with high blood pressure who are trying to lose weight:

“If people have high blood pressure and a weight problem, a low-carbohydrate diet might be a better option than a weight loss medication,” said Yancy, who is also a staff physician at the VA center in Durham where the study was conducted.

“It’s important to know you can try a diet instead of medication and get the same weight loss results with fewer costs and potentially fewer side effects,” he explained.

Previous research had already shown that both diets: prescription-strength orlistat (Xenical from Roche) combined with a low-fat diet, and a low-carb diet, were effective for weight loss.

But no study had pitched them head to head before, which the researchers said was a significant oversight since orlistat is now available over the counter as Alli, from GlaxoSmithKline. Plus, there is scarcely any evidence-based information to help overweight patients with chronic health issues, they added.

Yancy said their year-long study was particularly interesting because the 146 overweight participants had a range of health problems familiar to people with obesity: diabetes, high blood pressure, high cholesterol and arthritis.

This was unusual because most people who take part in weight loss studies are generally in good health and don’t have these problems, “in fact they are often excluded if they have,” said Yancy.

The results of the study showed that the average weight loss for participants in both groups (the orlistat with low-fat diet group and the low carb diet group) was nearly 10 per cent of their body weight.

Yancy said that not many studies reach that level of weight loss. He reckons this study managed it because the participants were offered group counseling for 48 weeks.

He also said that the participants tolerated orlistat better than he expected. The drug often has gastro-intestinal side effects that can be offputting (oily and loose stools with excessive flatulence due to unabsorbed fat reaching the large intestine), but these can be minimized by following a low fat diet, said Yancy.

“We counseled people on orlistat in our study fairly extensively about the low-fat diet,” he explained.

The two diets were also equally effective at improving cholesterol and glucose levels, said the researchers, but the surprise came when they looked at the results for blood pressure.

Systolic blood pressure dropped considerably in the group following the low-carb diet compared to the orlistat plus low-fat diet group.

Plus, almost half (47 per cent) of the participants following the low carb diet either reduced their blood pressure medication or were able to come off it altogether, while in the orlistat plus low-fat diet group the result was much less dramatic: only 21 per cent experienced a reduction in blood pressure medication.

Yancy said he expected both methods to result in significant weight loss, but he and his team were surprised to see such a dramatic improvement in blood pressure in the low-carb as opposed to the orlistat, low-fat diet group. He said he doesn’t know what the underlying mechanism could be: it’s not clear why or how it happened.

Perhaps the low-carb diet has an added effect, said Yancy, and there should be more studies to see what it might be.

Yancy said this study adds to the growing evidence that many diets are effective for losing weight, but the biggest impact appears to be in counseling patients to help them understand their options and how to follow them.

He said finding new ways to help people maintain their new lifestyle was even more important.